Hydrolysis of inositol trisphosphate by purified rat brain myelin

Prevention of rotavirus infections in vitro with aqueous extracts of Quillaja Saponaria Molina

BACKGROUND

Rotavirus is the leading cause of severe diarrhea disease in newborns and young children worldwide, estimated to be responsible for over 300,000 childhood deaths every year, mostly in developing countries. Rotavirus-related deaths represent approximately 5% of all deaths in children younger than 5 years of age worldwide. Saponins are readily soluble in water and are approved by the US FDA for inclusion in beverages intended for human consumption. The addition of saponins to existing water supplies offers a new form of intervention into the cycle of rotavirus infection. We believe that saponins will 'coat' the epithelium of the host's small intestine and prevent attachment of rotavirus.

DISCUSSION

This experiment provides in vitro data for the possibility of including saponin in drinking water to prevent infections of rotavirus. We demonstrate that microgram amounts of extract, while exhibiting no cell cytotoxicity or direct virucidal activity, prevent rotavirus from infecting its host cells. In addition, the presence of residual amounts of extract continue to block viral infection and render cells resistant to infection for at least 16 h after the removal of the extract from the cell culture media.

CONCLUSION

We demonstrate that two Quillaja extracts possess strong antiviral activity at concentrations more than 1000-fold lower than concentrations exhibiting cell cytotoxicity. Extract concentrations as high as 1000 μg/ml are not cytotoxic, but concentrations as low as 1.0 μg/ml are able to block rotavirus and reovirus attachment and infection.

Antiviral activity obtained from aqueous extracts of the Chilean soapbark tree (Quillaja saponaria Molina)

Natural, aqueous extracts of Quillaja saponaria, the Chilean soapbark tree, contain several physiologically active triterpenoid saponins that display strong adjuvant activity when used in either human or animal vaccines. In this paper, we describe studies that demonstrate a novel antiviral activity of Quillaja extracts against six viruses: vaccinia virus, herpes simplex virus type 1, varicella zoster virus, human immunodeficiency viruses 1 and 2 (HIV-1, HIV-2) and reovirus. We demonstrate that microgram amounts of extract, while exhibiting no cell cytotoxicity or direct virucidal activity, prevent each of the six viruses tested from infecting their host cells. In addition, the presence of residual amounts of extract continue to block virus infection and render cells resistant to infection for at least 16 h after the removal of the extract from the cell culture medium. We demonstrate that a Quillaja extract possesses strong antiviral activity at concentrations more than 100-fold lower than concentrations that exhibit cell cytotoxicity. Extract concentrations as high as 100 microg ml(-1) are not cytotoxic, but concentrations as low as 0.1 microg ml(-1) are able to block HIV-1 and HIV-2 virus attachment and infection.

The phosphoinositide signaling cycle in myelin requires cooperative interaction with the axon

Previous studies on the origin of myelin phosphoinositides involved in signaling mechanisms indicated axon to myelin transfer of phosphatidylinositol followed by myelin-localized incorporation of axon-derived phosphate groups into phosphatidylinositol 4-monophosphate and phosphatidylinositol 4,5-bisphosphate. This is in agreement with other studies showing the presence of phosphorylating activity in myelin that converts phosphatidylinositol into the mono-and diphospho derivatives. It was also found that the second messenger, inositol 1,4,5-trisphosphate, is hydrolyzed to inositol 1,4-bisphosphate by a myelin-localized enzyme. The present study was undertaken to determine the locus of the remaining reactions leading to formation of free inositol and completion of the cycle by resynthesis of phosphatidylinositol. The latter reaction was found to occur preferentially in isolated axons, and to a limited extent if at all in myelin. On the other hand, hydrolytic reactions which sequentially convert inositol 1,4,5-trisphosphate to inositol 1,4-bisphosphate, inositol 1-phosphate, and free inositol were found to occur more prominently in myelin. Thus, restoration of phosphoinositides following signal-induced breakdown of PIP2 in myelin is seen as requiring metabolic interplay between myelin and axon.

Biochemistry of demyelination

The myelin sheath, a lipid-rich multilamellar membrane of relative stability, both insulates and enhances conduction in nerve axons. A notable feature of myelin-specific proteins, in particular myelin basic protein, is their susceptibility to proteolytic activity and their encephalitogenicity, which induces inflammatory demyelination in the CNS. The final common pathway of myelin breakdown in vivo is well documented and there is evidence that myelin disruption can be mediated directly by soluble (circulating) factors and for following receptor-driven phagocytosis by macrophages. However the exact mechanism(s) of demyelination in multiple sclerosis is still unresolved, both antigen-specific and--non-specific events having the potential to generate the myelinolytic process.